Field of the Invention
The present invention relates to a process for preparing 4-isothiazolin-3-one, in particular to improved method for selectively preparing 4-isothiazolin-3-one having the following structural formula(I) which is useful as an antiseptic or anti-infectives in the field of cooling waters or metal processing oils for industrial, paints, cosmetics, sufactants, sensitizers. etc. ##STR2## wherein. R.sup.1 is methyl or n-octyl group:
R.sup.2 is hydrogen or chlorine atom. PA1 X is halogen atom.
European Patent Publication No. 0095907 discloses a method for manufacturing 4-isothiazolin-3-one derivatives as a mixture of two substance by carring out amidation reaction in accordance with the following scheme(A) and cyclization reaction of the following scheme(B). ##STR3##
Also, Journal of Heterocyclic Chemistry, 1971, 8 discloses a synthetic method of 2-t-octyl-4-isothiazolin-3-one having structure being similar to the above formula(I), by carting out amidation reaction in accordance with the following scheme(C) and chlorization and cyclization according to the following scheme(D). ##STR4##
But, according to the method of European Patent Publication No. 0095907, mixture of two substance, 2-methyl-4-isothiazolin-3-one of the above formula(a) and 5-chloro-2-methyl-4-isothiazolin-3-one of the above formula(b), is manufactured as a necessary, and then 5-chloro-2-methyl-4-isothisolin-3-one of the formula(b) has higher virulence than the formula(a).
Therefore, the product mixed cannot be used for the human body, and cannot be used for a long time because of being stability at room temperature and so used within the limits. Also, the yield is low.
Nevertheless, a method for selectively preparing or separating the formula(a) has not been developed, and if it may be separated, the process is intricate and uneconomical. So, the mixed product has been used as it is.
The method disclosed in Journal of Heterocyclic Chemistry is to prepare 2-t-octyl-4-isothiazolin-3-one by using Cl.sub.2 gas and toluene as solvent on the scheme(D), but the product is not the compound of structure having n-octyl group.